Sound reproducing system



Aug 10, 1937. J. H. HAMMOND, JR 2,089,792

SOUND REPRODUC ING SYSTEM 4Filed Dec. 21, 1955 2 sheets-sheet 1 d I w @5% /Q Aug.` 10, 1937.

J. H, HAMMOND, JR 2,089,792

SOUND REPRODUC ING SYS TEM Filed Dec. 2l, 1933 2 Sheets-Sheet 2 Snow/tto@ Patented Aug. 10, 1937 UNITED STATES PATENT- OFFICE SOUND REPRODUCING SYSTEM John Hays Hammond, Jr., Gloucester, Mass.

Application December 21, 1933, Serial No. 703,339 z claims. (ci. -ris- 1003) This invention relates to sound reproducing systems, and more particularly to means for coritrolling the volume of sound reproduced from a sound record b'y means of a control channel which receives energy from said record.

According to one form of the invention, a control channel is provided with a secondary pick-up device separate from the pick-up for supplying energy to the sound amplifying system from the sound track. This secondary pick-up may precede the usual pick-up in the sound track whereby operation of the control channel is initiated by the sound record in advance of the amplification of the sound. The amplifier may also be l5 provided with additional means for varying its amplification.

One of the difjculties of such volume control systems as have been devised in the past has been that the control means for varying the ratio of sound pick-up to out-put of sound energy from the amplifier possessed a certain delay in their operation whereby the degree of amplification was changed at some time later than the actual variation of volume of sound input.

The present invention makes possible the initiation of operation of the control channel in advance of the actual pick-up of sound by the ampliiier system whereby the delay in the operation of the control channel can be overcome and the amplifier may be preset according to the volume of sound it is to amplify. The invention is applicable, for example, to systems for increasing the volume range on reproducing from a sound record whereby the loud tones and their accompanying overtones are amplified to a greater extent than the soft tones.

The invention also consists in certain new and original features of construction and combinations of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof, in which Fig. l illustrates diagrammatically the system as applied to a moving picture projector and to a phonograph.

Fig. 2 illustrates diagrammatically the amplifying and controlling systems associated with the parts show n in Fig. 1,

Like reference characters denote like parts in the several figures of the drawings.

1n the following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic 5 in their application to similar parts as the art will permit.

Referring more particularly to the form of the invention shown in the accompanying drawings,

a phonograph mechanism III is provided with the 10 usual turn table I I upon which is placed a record I2. Engaging the sound track of this record are two needles I3 and I4 which are mounted in pickup devices I5 and I6 carried on the ends of arms Il and I8. The arms Il and IB are pivoted to 15 two niembers 2I and 22 which are rotatably mounted upon the casing of the phonograph mechanism I0. The primary pick-up device I5 isccnnected to two contacts 23 and 24 of a doublepele double-throw switch 25. The secondary pick-up device I5 is connected to two contacts 25 and 21 of a second double-pole double-throw switch 28.

A moving picture projector 3I is provided with the usual film 32 which passes over sprockets 33 25 and behind two apertures 34 and 35 provided in the casing of the projector 3|. In front of these apertures are mounted two lenses 3B and 31 which focus the light from two lamps 38 and 3S through apertures 34 and 35 and upon the sound track of the film 32. On the other side of the lm 32 and in line with the apertures 34 and 35 are two lenses 4I and 42 which focus the light which passes through the film 32 upon two photo-electric cells 43 and 44. The photo-electric cell 43 3- is connected to two contacts 45 and 45 of the switch 28 and the photo-electric cell 44 is connected to two contacts 4l and 48 of the switch 25.

The switch 25 is connected by two conductors 5I and 52 to the primary of a transformer 53 the 40 secondary of which is connected to a potentiometer 54. The adjustable contact of this potentiometer is connected to the input circuit of a space discharge means 55 and through a blocking condenser 56 to the input circuit of a second 45 space discharge means 5l.

The output circuit of the device 51 is connected to the primary of a transformer 58, the secondary of which is connected through a rectifier 59 to a resistance 6I which is in the grid return of the 50 space discharge means 55. A condenser 62 is shunted across this resistance.

The output circuit of the space discharge means 55 is connected through a transformer 63 to the input circuit of a push-pull amplifier 64, 55

the output circuit of which is connected through a transformer 65 to the moving coil of a loud speaker 66. The field winding 61 of this loud speaker is energized by a battery 68.

5 The blades of the switch 28 are connected by two conductors 1I and 12 to the primary of a transformer 13 the secondary of which is connected to the input circuit of an amplifier 14, the output circuit of which is connected through a transformer 15 to the input circuit of a pushpull amplifier 16. The output circuit of this amplier is connected through a transformer 11 to two resistances 18 and 19, the other sides of which are connected through a transformer 8| to a rec- 15 tifier 82 the output circuit of which is connected to the input circuit of two space discharge means 83 and 84. The plate circuits of these devices are connected to the secondary of a. transformer B5, the primary of which is connected to a source of A. C. supply 86. A small secondary 81 is provided for supplying the filament current for the devices 83 and 84.

To the center point of the secondary of the transformer 85 is connected one side of the winding of a solenoid 9|, the other side of which is connected to the filament circuit of the devices 83 and 84 and to the rectifier 82. The solenoid 9| is provided with a core 92 which is pivoted to one end of an arm 93 which is rotatably mounted on a fra-me 84. The other end of the arm 93 is pivoted to one end of a rod 95, to the other end of which is attached the movable contact of the potentiometer 54.

In the operation of the form of the invention shown in the accompanying figures, when it is desired to use the phonograph I' the switches 25 and 28 are thrown down thus connecting the pickup device I to the transformer 53 and the pickup device I6 to the transformer 13. When the record is played, the pick-up device I6 transmits energy through the transformer 13 to the amplifiers 14 and 16 where this energy is amplified and passes through the transformers 11 and 8|, to the rectifier 82. Here the current is rectified and 45 caused to produce a positive bias on the space discharge means 83 and 84, thus increasing the output of these devices which in turn increases the current passing through the solenoid 9|. The rectified current and hence the current through 50 the solenoid is dependent upon the strength of the signal picked up by the pick-up device I6. The output current of space discharge means 83 and 84 energizes the solenoid 9| causing the core 92 to be moved downward an amount dependent 55 upon the strength of this current. This in turn rotates the arm 93 in a clockwise direction thus causing the rod 95 together with the contact of a potentiometer 54 to be moved upward. It is thus seen that the amount of energy picked up by the 60 potentiometer 54 will be dependent upon the strength of the signal at the needle I4 in the groove of the phonograph record I2. The potentiometer 54 will be adjusted, however, at a length of time after the sound energy is picked up by 65 needle I4 which depends upon the time necessary for the operation of the control channel.

The pick-up device |5 transmits its energy through the transformer 53 to the potentiommeter 54 where, as already described, the amount 70 of energy transmitted t0 the amplifier is dependent upon the strength of the signal in the sound track at the point where the needle of the pick-up device I6 rested at a slightly earlier time, dependent upon the delay introduced by the 75 control channel. The energy from the potentiometer 54 then passes to the input circuit of the space discharge means 55. Some of the energy also passes to the input circuit of the space discharge means 51. The energy from the output circuit of this device then passes through the transformer 58 and is rectified by the rectifier 59. This rectified current then passes through the resistance 6I causing a potential difference to be built up across this resistance which is dependent upon the strength of this current and therefore upon the amount of energy picked up from the potentiometer 54. This potential across the resistance 6I causes a decrease of bias on the-device 55, thus decreasing its impedance and therefore increasing the amplification ratio. It is thus seen that the amplification ratio of this amplifier is dependent upon the signal strength and therefore is greater for signals of greater strength.

The output energy from the space discharge means 55 passes through the transformer 63 to the input circuit of the push-pull amplifier 64 where it is further amplified and passes through the transformer 65 to the moving coil of the loud speaker 66 which reproduces the speech or music in a well-known manner.

It is evident, therefore, that if the control pick-up device I6 is located a short distance ahead of the sound pick-up device I5, that the operation of the controls will be initiated at such time or, if desired, slightly in advance of the time when the corresponding sound would be picked up by the pick-up device I5. By suitably proportioning the distance between the needles I3 and I4 and the constants of the circuits, it is possible to have the system work so that there is no appreciable lag in the control mechanism. If this feature were not provided it would be found that there would be a noticeable lag in the response of the amplifying system to volume changes and this would produce an unpleasant effect upon the listener.

If it is desired to use the moving picture projector 3| the switches 25 and 28 are thrown up thereby connecting the photo-electric cell 43 to the transformer 13 and the photo-electric cell 44 to the transformer 53. The film 32 is moved in the usual manner, and as any part of it passes the openings 34 and 35 in succession it controls the light passing from the lamps 38 and 39 to the photo-electric cells 43 and 44. 'Ihe energy from these cells then passes to the transformers 13 and 53 respectively. From here on, the operation of the device is essentially similar to that described in connection with the phonograph. It is thus seen that the intensity of the sound record causes the solenoid 9| to set the control potentiometer 54 slightly in advance of the reception of the energy from the photoelectric cell 44 which produces the sound or music as already described in connection with the phonograph mechanism.

Although only a few of the various forms in which this invention may be embodied have been shown herein, it is to be understood that the invention is not limited to any (specific construction, but might be embodied in various forms without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is:

1. In a system for reproducing sound from a single sound record track, a primary pick-up device for sound, a sound propagating device fed by said pick-up device, a secondary pick-up device for control, control means fed by said secondary pick-up device having means to vary the volume of sound produced'by said sound propagating device in accordance with the changes in recorded volume so as to compensate for the volume compression inherent in said record track, said secondary .pick-up device being located on said track a predetermined .distance in advance of said primary pick up device such that control of said amplier is effected thereby prior to the reception of the corresponding sound energy 10 by said amplifier.

2. In a system for reproducing sound from a sound record tablet having a single sound track, a primary pick-up device for sound, a sound propagating device fed by said pick-up device, a

JOHN HAYS HAMMOND, JR. 

